Large scale steerable coherent optical switched arrays

ABSTRACT

Aspects of the present disclosure describe large scale steerable optical switched arrays that may be fabricated on a common substrate including many thousands or more emitters that may be arranged in a curved pattern at the focal plane of a lens thereby allowing the directional control of emitted light and selective reception of reflected light suitable for use in imaging, ranging, and sensing applications including accident avoidance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/457,158 filed Jun. 28, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/927,037 filed Mar. 20, 2018, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 62/473,689 filed20 Mar. 2017, each of which are incorporated by reference as if setforth at length herein.

TECHNICAL FIELD

This disclosure relates generally to beam steering of light and moreparticularly to large scale optical phased arrays (OPA) that steercoherent light.

BACKGROUND

Recent advancements in silicon photonics fabrication technologies hasprecipitated the development of nanophotonic optical arrays that haveproven useful in a number of contemporary applications including lightdetection and ranging (LiDAR), free space communications and holographicdisplays. Given their utility, further development and/or improvement ofnanophotonic optical arrays would represent a welcome addition to theart.

SUMMARY

An advance in the art is made according to aspects of the presentdisclosure directed to large scale steerable optical switched arraysthat may be advantageously fabricated on a common substrate and includemany thousands or more emitters.

In illustrative embodiments the emitters may be arranged in a curvedpattern at the focal plane of a lens thereby allowing the directionalcontrol of emitted light and selective reception of reflected lightsuitable for use in imaging, ranging, and sensing applications includingaccident avoidance.

BRIEF DESCRIPTION OF THE DRAWING

A more complete understanding of the present disclosure may be realizedby reference to the accompanying drawing in which:

FIG. 1 is a schematic diagram illustrating emitters positioned on acurved focal plane radiate collimated beams in different directions into a far field according to aspects of the present disclosure;

FIG. 2 is a schematic diagram illustrating a configuration of a photonicswitched array tree in which power from a laser is switched between thearms of the tree and each emitter receives the total power at sequentialinstances in time according to aspects of the present disclosure;

FIG. 3 is a series of timing diagrams illustrating switching voltagesrequired for the first three stages of a power delivery tree for theillustrative configuration depicted in FIG. 2 according to aspects ofthe present disclosure;

FIG. 4 is a schematic showing an illustrative switched array treewherein voltage controlling stages having multiple switches may bedivided among more than one pad/wire to reduce current required andpower consumption according to aspects of the present disclosure;

FIG. 5 is a schematic showing an illustrative switched array treewherein faster switches employed in earlier stages and proper sequencingallows for slower switches at later stages according to aspects of thepresent disclosure;

FIG. 6 is a series of timing diagrams illustrating that switching timeconstant(s) of higher level switches may be longer than in prior stagesaccording to aspects of the present disclosure;

FIG. 7(A) is a schematic of an illustrative switched array tree showinga same switched array function as both emitter and collector element(monostatic) according to aspects of the present disclosure;

FIG. 7(B) is a schematic of an illustrative switched array tree showinga same switched array function as both emitter and collector element andfurther including a circulator to separate the transmit (emitter) andreceive (collector) signals according to aspects of the presentdisclosure;

FIG. 7(C) is a schematic of an illustrative switched array tree andlaser light source wherein the emitters emit light out of planeaccording to aspects of the present disclosure;

FIG. 7(D) is a schematic of an illustrative switched array tree andlaser light source wherein the emitters emit light out of plane and amulti-lens system is employed to provide a “flat” focal plane accordingto aspects of the present disclosure;

FIG. 8(A) is a schematic of an illustrative switched array tree showinga two-lens configuration of a switched array using for pulsed (flash)LiDAR wherein an array of detectors are employed that are not part ofthe switched array according to aspects of the present disclosure;

FIG. 8(B) is a schematic of an illustrative switched array tree as shownin FIG. 8(A) wherein transmitted signals are reflected from two objectsin object space and the reflected light is detected from multiple,corresponding detectors in the detector array according to aspects ofthe present disclosure;

FIG. 9 is a schematic of an illustrative switched array tree showing atwo lens and two tree configurations for LiDAR according to aspects ofthe present disclosure;

FIG. 10 is a schematic showing an illustrative two lens system whereinsend and receive signals can be at different angles in the far fielddepending on the distance of an object from a LiDAR system according toaspects of the present disclosure;

FIG. 11 is a schematic showing an illustrative use of a focusing gratingat an output of a switching tree enabling fine adjustments of spotlocation thereby enhancing far field scanning according to aspects ofthe present disclosure;

The illustrative embodiments are described more fully by the Figures anddetailed description. Embodiments according to this disclosure may,however, be embodied in various forms and are not limited to specific orillustrative embodiments described in the drawing and detaileddescription.

DESCRIPTION

The following merely illustrates the principles of the disclosure. Itwill thus be appreciated that those skilled in the art will be able todevise various arrangements which, although not explicitly described orshown herein, embody the principles of the disclosure and are includedwithin its spirit and scope.

Furthermore, all examples and conditional language recited herein areintended to be only for pedagogical purposes to aid the reader inunderstanding the principles of the disclosure and the conceptscontributed by the inventor(s) to furthering the art and are to beconstrued as being without limitation to such specifically recitedexamples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the disclosure, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat any block diagrams herein represent conceptual views ofillustrative circuitry embodying the principles of the disclosure.

Unless otherwise explicitly specified herein, the FIGs comprising thedrawing are not drawn to scale.

By way of further background and it is noted that—in general—an “ideal”single lens imaging plane is not flat. Such a principle was noted asearly as the 19^(th) century by Joseph Petzval—among others—and is usedby photographers to capture images having an in-focus central portionand a sharply out-of-focus periphery. As a more specific example, theimage sensor array of state-of-the-art, modern telescopes—such as theKepler space observatory—is curved.

As will be known and appreciated by those skilled in the art—based ontime reversal symmetry—if an array of light emitters is positioned on acurved focal plane of a lens, light beams emitting from all the emittersare imaged to infinite distance (and therefore are collimated) but atdifferent angles.

Such principle is shown in FIG. 1 which shows a schematic illustratingthe placement of optical emitters (i.e., lens(es) such as the doubleconvex lens shown) positioned on a curved focal plane radiate collimatedbeams in different directions in to a far field. While not specificallyshown in this FIG. 1, it is noted that through judicious choice(s) ofoptical elements (lenses) the shape of the focal plane may be altered toone that is flatter. Such a flat focal plane in conjunction withsuitable optical elements including lenses is shown and described later.

With these principles in mind, turning now to FIG. 2, there is shown aschematic diagram of an illustrative, basic, photonic switched arraytree. As may observed from that figure, an array of emitters is inoptical communication with a light source (laser) through the effect ofa switched array tree comprising a plurality of 1×2 switches arranged inan uprooted tree topology. Depicted in that figure, output power from alaser is switched between arms of the tree through the effect ofswitches in response to applied voltage(s). As will be readilyunderstood by those skilled in the art, the switches (for example,Mach-Zehnder interferometers) may be optically interconnected by any ofa variety of known optical waveguides that—in an illustrativeembodiment—may be integrated onto a silicon photonic substrate alongwith the emitters.

Operationally, each illustrative individual switch in the tree ofswitches is controlled by the application of a suitable voltage.Accordingly, the three-level tree of switches shown illustratively inFIG. 2 delivers optical power emitted from a laser to a designatedemitter, or—as we shall show—emitters.

At this point it is noted that while we have shown and described thisillustrative configuration as employing a switched array tree having 1×2switches, our disclosure is not to be considered so limiting. Morespecifically, any configuration of switches are contemplated (i.e., 1×3,1×4, . . . , 2×2, 2×3, . . . etc). The tree illustrated is a topologyknown in the art, that is there are no circular paths between nodes(switches). As we shall show and describe further, the switch type(s) ina particular switched array tree need not all be of the same type, ortechnology (i.e., thermos-optic, electro-optic, etc.).

Worth noting further at this point is that the emitters employed maylikewise be a variety of those known in the art. Optical emitters thatmay advantageously be employed according to the present disclosureinclude—for example—an optical grating, end-fire facet, plasmonicemitter, metal antennae, and mirror facet—among others.

Starting from the laser, the very first switch (SW1-1—firstlevel—controlled by V1) directs light output by the laser to the upperor lower half of the switch array tree. Accordingly, at the secondlevel, only one of the two switches (SW2-1, SW2-2)—both of which arecontrolled by V2—receive light output from first level switch dependingon how the first level switch is controlled by V1. Even though in anideal case the switches controlled by V2 are identical and the voltagerequired to control them is equal, in a practical system these will beslightly different from each other—and from V1 as well.

The same is true for the third level switches. All four of them areidentical by design but will have slightly different voltagerequirements for perfect (0%-100%) power switching between its twooutput ports. It is noteworthy that even though these switches require avoltage which is slightly different from their neighbor, they do notrequire a separate wiring. This is due to the fact that in thisillustrative example only one of the switches at a given level isreceiving light at any moment in time. Accordingly, the state(s) of theother switch(es) at that level are of no consequence.

Turning now to FIG. 3, there is shown a series of timing waveformsshowing switching voltages required for the first three stages of anoptical power delivery tree such as those illustratively shown anddescribed herein. As can be seen in FIG. 3, V1 switches between theoptimal values for the first switch (SW-1-1). V2, controls all theswitches on the second-level (SW-2-1, SW2-2) changes value at twice thefrequency of V1.

As may be observed and understood, in first half period (0−T/2), thefirst switch directs light to the upper half of the array i.e., toSW-2-1. From the discussion above we know that during that first halfperiod of time, the uppermost second level switch (SW-2-1) goes betweenthe values optimized for that switch and drives the other, lower secondlevel switch (SW-2-2) with it redundantly.

As will be readily appreciated by those skilled in the art, this simple,illustrative scheme—while not being the most power efficient method todrive the switched array tree—greatly simplifies the overall system withrespect to the number of I/O pads and control signals required tocontrol the switch tree. More specifically, an array tree of Nelements—when configured in this simple manner—requires only log 2(N)control signals rather than N−1 control signals if each switch had itsindividual wiring and I/O pad. As will be further appreciated by thoseskilled in the art, this simple illustrative configuration results in atleast half of the switches in the tree consuming power while only log2(N) of them are switching (directing) light at any given time.

Note, however, that if overall power consumption and current delivery ofthe switch tree array is more important than the number of I/O padsrequired, a smaller number of the switches can advantageously be wiredin parallel. With reference now to FIG. 4—that shows an illustrativeswitched array tree wherein voltage controlling stages (levels) havingmultiple switches may be divided among more than one pad/wire to reducecurrent required and power consumption according to aspects of thepresent disclosure.

For example, as can be seen in FIG. 4, the V3 control signal—used tocontrol third level switches SW-3-1, SW-3-2, SW-3-3, SW-3-4, may bedivided into two separate signal voltages. In this illustrativesituation, at time period 0-to-T/2 illustrated in FIG. 3—when only thetop half of the array is used (determined by V1)—all of the switchesused at the third level of the array that are not functioning (SW-3-3,SW-3-4) can be set to zero power. Therefore, by adding one I/O pad(V3_B) the overall power consumption is reduced.

As will be readily appreciated by those skilled in the art, a designtradeoff results from these illustrative, alternative configurations.Extra I/O pad(s) and interconnecting circuits are required to providethis improved, reduced power consumption. Such design tradeoff's may beadvantageously made on a case-by-case basis.

Note that a large area switch tree array and corresponding phased array(several millimeters or larger across) with elements spaced near (orsmaller than half wavelength) apart, will contain thousands of elements.Such a switched array tree will have ten or more levels of switchingbefore light reaches an emitter. Accordingly, a necessary designtradeoff must be made in such a situation between the number of I/Osignals employed—which is at least 10-20 and can reach thousands if eachswitch is addressed individually—and the power consumption that canscale inversely with the number of I/O signals/pads employed.

As we shall now describe, another aspect of a switched arrayarchitecture according to the present disclosure is that the time scaleand the power consumption of different switch layers in the array is notnecessarily the same. FIG. 5 is a schematic showing an illustrativeswitched array tree wherein faster switches employed in earlier stagesand proper sequencing allows for slower switches at later stagesaccording to aspects of the present disclosure.

As may be observed from that FIG. 5, the array can be operated in amanner that the time between neighboring emitters receiving light ismaximized. In such a scenario, two neighboring emitters may be selectedbetween the two neighbors by a single, slow switch. Such a configurationis made possible due to a switch at the last level has a significantlylonger time to change its state as compared with prior level switchesbecause it only sees light at a fraction of time and the time in betweenthose instances can be used for a slow (but possibly low loss or lowpower) transition. Note further that such operation permits a selectionof emitter(s) that are not necessarily sequential. In this illustrativedepiction, the topmost emitter (1) is selected, then others (2), andthen (3) which are not in physical, sequential order of the array.

FIG. 6 is a series of timing diagrams illustrating that switching timeconstant(s) of higher level switches may be longer than in prior levels(stages) according to aspects of the present disclosure. For example,FIG. 6, shows a scenario in which the first two levels of the switchtree array are controlled by fast switches. The third level of the treehas a much slower switch which receives light only when the first switchand the second switch are in a high-state (grey areas). In thissituation, the switch controlled by V3_A (SW-3-1)—shown in in FIG.5—which is responsible to direct light to either emitter of the firstneighboring emitters (1 or 2), can be significantly slower in transitionthan the first two switches because it does not receive light outside ofthe shaded regions of the timing diagram of FIG. 6.

Advantageously, and as will be readily understood and appreciated bythose skilled in the art, physical mechanisms employed for lower andhigher levels of switches can be different. Note that with respect tothe above discussion, first level(s) of switches only transition betweenon/off/up/down states a few times per total array scan but hold eachstate for extended periods of time (as long as T/2 for the first levelswitch). On the other hand, the later or last level(s) of switches(i.e., final branches of the switch tree) can be in transition each timea far field point of view changes. Consequently, initial levels (stages)of the tree can utilize switches that consume more power in thetransition state (like reverse biased pn junction based electroopticphase shifter Mach-Zehnder switches), while end branch levels of thetree can utilize switches that consume power only when they are in aswitching mode (i.e., on/off or up/down transition) and not in the reststate (e.g., thermooptic or electrooptic switches).

At this point we may now describe how systems, methods and structuresaccording to the present disclosure may operate in illustrativeapplications. With simultaneous reference now to FIG. 7(A) and FIG.7(B), there is shown a schematic diagram illustrating a switched arraystructure according to the present disclosure employed as part of aLIDAR wherein the same switched array functions as both emitter andcollector element(s). As we shall show and describe, suchconfiguration(s) may be generally known as “monostatic” configurationsas the same emitter/aperture is used for both transmit/receivefunctions.

Accordingly, and as shown schematically in the figures, the switchedarray, operates as a transmit and receive component of a LiDAR or a freespace communications system. Illustratively, a frequency-modulatedcontinuous wave laser detection and ranging (FMCW) LiDAR system isillustratively shown wherein the same array simultaneously functions asa send and receive element due to the time symmetry of nonmagneticoptical systems.

As will be readily understood and appreciated by those skilled in theart, light travelling along a certain path—when scattered and/orreflected by an object—will have a portion of that scattered lighttravel the exact same path—in reverse—where it may be detected at theorigin.

With reference to that FIG. 7(A) and FIG. 7(B), it may be observed thatan array of emitters is optically interconnected to a laser light sourcethrough the effect of a switched tree array or other analogousdistribution network. As illustrated in those figures, each level of theswitch array is shown illustratively controlled by a signal voltage,i.e., V1 for level 1, V2 for level 2, and V3 for level 3 switch(es).Selective application of the level voltages to the particular levelswitch(es) will direct light emitted from the laser to a particularemitter.

Shown interposed between the laser source and the switch array, is anillustrative 2×2 switch (FIG. 7(A))—or alternatively, an opticalcirculator (FIG. 7(B)). Such redirector (switch or circulator) providesthe optical communication for a laser reference and—as we shalldiscuss—a return(ed) signal—both of which are directed through theeffect of the redirector to a detector—i.e., coherent detector in thisillustrative example.

Operationally—and by way of specific illustrative example only usingFIG. 7(A) and not in any way limiting—laser light is emitted from thelaser source and received by the 2×2 switch. A portion of that receivedsource light is directed to a coherent detector where it serves as areference for coherent detection processes. Another portion of thatreceived source light is directed to a switched tree array distributionnetwork. As previously noted and discussed, specific application ofswitches comprising the switched tree array distribution network directthat source light to a specific emitter, where it is emitted andpossibly subsequently reflected by an object situated in object space.

As noted further previously, a portion of that reflected light willtravel the same path traversed after emission—in reverse. That reflectedlight so traveling the reverse path will be collected by a same emitteras transmitted, directed back through the switched tree array to the 2×2switch (redirector), where it is directed to the coherent detector fordetection. In this way, the same path through the switched tree arraydistribution network is bidirectional—that is provides both transmit andreceive path(s). As noted above, such a configuration may be known asmonostatic.

We note at this point that as shown schematically in FIG. 7(A) and FIG.7(B) a lens or other optical element is shown in the optical path of theemitted light at the emission side of the emitters to furtherdirect/collect transmitted/received light as appropriate. Suchlens/optical element may be any of a variety that directs/collects lightas desired. Note further that while a single lens is shownillustratively, a different number of lens(es)/optical elements arecontemplated and may include—for example—an array of such lenses/opticalelements. In particular embodiments, such optical elements may serve toflatten the focal curvature of the emitter array.

In particular, while we generally have shown the array of emitters asarranged along a curved arc substantially at a focal point of theexternal lens, our disclosure is not so limited. More particularly, withan appropriate choice of lens—i.e., a double convex lens—the focal planewill flatten. As such, the array of emitters may be positioned along aline that is not curved—provided additional, appropriate opticalelement(s) (lenses) are interposed in an optical path after the emitters(distal).

As will be understood, the configuration shown in FIG. 7(A), will havethe advantage of simplicity of design and operation but can suffer fromon-chip reflections from the switching elements, the emitters and anylens(es). Accordingly, the configuration shown and described withrespect to FIG. 7(B) in which the switch is replaced by a circulatorwill mitigate these disadvantageous reflections.

FIG. 7(C) is a schematic diagram showing an illustrative example of alaser in optical communication with a plurality of emitters through theeffect of a switched array wherein the emitters are configured to emitout of plane. Note that while this illustrative switched array shown inthis figure—while employing a plurality of individually controllable 1×2switches—such configuration is not necessarily required according to thepresent disclosure. In particular, alternative switch configurations maybe employed with the condition that no circular paths between source andemitter is produced. Note further that all of the other aspects we havedescribed namely, individual levels, single electrical pad controllingmultiple switches at a given level, etc., are all contemplated with thisillustrative configuration as well.

FIG. 7(D) is a schematic showing an illustrative flat focal plane forthe out of plane configuration illustrated in FIG. 7(D) in which amulti-lens system is employed in an optical path of the emitted light.As described previously and illustratively shown schematically in thisfigure, such optical elements positioned in the optical path afteremission may produce such a flat focal plane.

FIG. 8(A) is a schematic diagram showing an illustrative alternative tothe configuration of FIG. 7(A) and FIG. 7(B) according to aspects of thepresent disclosure that may advantageously be employed—for example—in apulsed or “flash” LIDAR application. As illustratively shown in FIG.8(A), one switched array is employed as an emitter element while a focalarray of detectors is employed as receiving element(s). Note that inthis illustrative configuration, the detector “array” may include only asingle detector—or a plurality of detectors as illustratively shown inthe figure. Note further that configurations such as that shown in FIG.8(A), and in FIG. 8(B), a distance between emitter and reflecting objectmay advantageously be determined in a number of ways.

As will be readily appreciated by those skilled in the art, such pulsedLiDAR systems and methods enable practitioners to sweep or scan largeareas while collecting billions of data points, each with preciselatitude, longitude, and elevation (x, y, z) values within a local(relative) coordinate system. This aggregation of the billions of datapoints is oftentimes referred to as a point cloud data set.Practitioners subsequently extract object locations from the point clouddata set and use that location information for subsequent decisionmaking.

Known further by those skilled in the art, point cloud data sets may becollected by a Geiger Mode Avalanche Photo Diode (GmAPD_-based LiDARsystems—a number of which are known in the art. Operationally,GmAPD-based LiDAR systems generally comprises a transmitter includinglaser transmitter(s) and transmitting optics, receiver includingreceiving optics and photo-detector(s), and processing system(s) (notspecifically shown in FIG. 8(A) or FIG. 8(B)).

When installed or otherwise mounted on movable platforms such as anautomobile, such LiDAR system(s) may be configured or individuallycombined to sweep or scan over a large volume such that a full360-degree environmental view may be made.

Accordingly, the transmitter periodically transmits interrogatingsignal(s) into a detection region from which they may be reflected backas return signal(s). Generally, the interrogating signal(s) are a trainof optical-pulses exhibiting a period and a wavelength and intensitysuitable for interrogating the detection region. The wavelength(s) ofthe interrogating signal(s) are oftentimes in the range of 900 nm to2000 nm however, other usable wavelengths are known in the art.

In an illustrative GmAPD-based LiDAR system embodiment such as thatillustrated in the figure, the transmitter will include a lasersource—such as a diode laser—which emits an optical pulse train ofinterrogating signal(s) in response to drive signal(s) from—forexample—a processing system (not specifically shown). As each opticalpulse of interrogating signal propagates through the detection region,objects reflect a portion of a pulse's optical energy back toward systemas reflected optical pulse(s) in receive (returned) signal(s) which maybe detected by a receiver.

In contemporary embodiments, the receiver may include an array of GmAPDdetector pixels. As will be readily appreciated and understood by thoseskilled in the art, one particular advantage of GmAPDs is that theyquickly produce an electrical pulse in response to the detection of evena single photon—allowing for sub-nsec-precision photon-flight-timemeasurements. When each pixel is armed, it may detect a low-intensityreflection of an interrogation signal (return signal) and output asignal to be detected and subsequently used by the processing system. Asshown illustratively in the figure, the array of detectors is positionedsubstantially at the focal plane of another (receiver) lens.

FIG. 8(B), shows a disparate detector array—like that shown in FIG.8(A), wherein emitted light is reflected from two distinct objectslocated in object space. Shown further in that figure, light reflectedfrom those objects are subsequently detected by multiple detectors inthe receiver detector array. Advantageously, when so configured, adistance between emitter/detector and object(s) may be determined bytriangulation or—alternatively—time of flight (TOF). Note further thatsuch configurations shown illustrative in FIG. 8(A) and FIG. 8(B) do notutilize or employ a return path that is the reverse of the transmit pathas shown previously with respect to monostatic configurations.

FIG. 9 shows a schematic of yet another illustrative system according tothe present disclosure illustrating a two lens and two switched treeconfigurations of an FMCW LiDAR system. As may be observed from thatfigure, such system includes two separate switched tree arraydistribution networks, one for transmit (send) and the other for receivesignals. Such configuration is known as a bistatic configuration as theemitting aperture and receiving aperture are not the same aperture.Notwithstanding this distinction, as we shall show, the emitting andreceiving apertures—while different—may be located at a same,corresponding position in an array. For example, in the illustrationshown in FIG. 9, the 7^(th) emitter in the emitter array is used and the7^(th) receiver (emitter) is used in the receiver array. Other,corresponding emitter/receiver pairs may be likewise employed.

At this point we note that while we have used the terms emitter andreceiver, such structures may exhibit the same—or different—structuralcharacteristics. For example, an “emitter” may comprise an end facetwhile a receiver may likewise comprise an end facet. That is to say,such emitters and receivers may be any suitable optical “antenna”. Notefurther that while such receivers may be constructed like any emittersuch as those identified earlier, a given emitter/receiver complementarypair do not have to be of the same construction. That is to say, anemitter may comprise a grating while a receiver may comprise an endfacet—or any other combination.

Continuing with our discussion of FIG. 9, there it may be observed alaser source provides transmit (interrogation) light to one of the twoswitched tree distribution networks while the other receives returnedand collected light from an object in interrogation space and directsthat light to a detector which, in this illustrative configuration isshown as a coherent detector.

As shown in this illustrative configuration, light emitted from aparticular emitter—in this scenario the 7^(th) emitter—will bereflected/scattered from an object and received by a corresponding7^(th) emitter/detector. As will be further understood by those skilledin the art, since the two switched tree distribution networks correspondto one another, a common set of control signals applied to each networkwill activate appropriate corresponding switches in each network forcomplementary emission/reception.

We note that such configurations that include two lenses (or multiplelens configurations or combinations thereof), or two lenses and twotrees, advantageously do not generally suffer from reflection effects ofthe single transmit tree (monostatic) configurations describedpreviously. In the illustrative example shown in the figure, the receivetree will receive the reflected/detected signal(s) and direct same tothe coherent detector. As illustrated, the coherent detector receives aportion of the laser power as a local oscillator thereby permittinginformation determination from/about time of flight data. Note that asillustrated a beat signal may be generated at a root of the receivingswitched tree by one coherent detector or at an end of the tree bymultiple local oscillators each receiving the local oscillator laserpower in turn by a switching tree.

As will now be readily understood and appreciated by those skilled inthe art, one feature of such two lens systems is the misalignment of thesend and receive beams. Turning now to FIG. 10, there is shown aschematic diagram illustrating that in a two-lens system, the send andreceive signals may be at different angles in the far field depending onthe distance of the object from the (LiDAR) system. As can be seen inFIG. 10, the closer the object is to the two-lens system, the moredivergence in the angles of the send and receive signal will appear.Therefor this misalignment should be taken into the account when twoswitched array trees are employed in a system such as that shown in FIG.9. As those skilled in the art will now readily appreciate, this featuremay advantageously be used for distance measurement (similar to depthperception of humans with the eyes located on the two sides of theface).

We note that for a one-dimensional integrated optics switched array theterminated end of the waveguides can function as a perfect, broadbandemitter without requiring a grating or any other sophisticated radiationmechanism. On the other hand, as the waveguides are placed a fewmicrometers apart from each other, far field operation of the arraybecomes more discrete (discretized) with the angular resolution beingdependent on the focal length.

One approach to improve this resolution is to change the wavelength ofthe laser slightly. With reference to FIG. 11, there is shown a focusinggrating positioned an optical path of light emitted from an emitter.More specifically, the focusing grating is positioned in the opticalpath of the emitted light after the emitter and before the object inobject space. A focusing grating positioned at the end of the switchedtree will focus the light into a spot however, the focusing point iswavelength dependent and therefore moves slightly with changingwavelength. If the tunability range of the laser is enough to move thefocal spot between the two original tree outputs, the far field viewingcapability of the array will be continuous with rough scanning achievedby the switching tree and fine movements achieved by the laserwavelength.

At this point, while we have presented this disclosure using somespecific examples, those skilled in the art will recognize that ourteachings are not so limited. In particular, while we have shown anddescribed various illustrative configurations employing switched binarytree distribution networks optically connecting a source to a pluralityof emitters, this disclosure is not so limited. In particular, aselectively, switchable distribution network of any size and topologybetween laser and emitter is contemplated and included in thisdisclosure. Accordingly, this disclosure should be only limited by thescope of the claims attached hereto.

The invention claimed is:
 1. An optical structure comprising: aplurality of optical waveguides integrated onto a photonic substrate; aplurality of optical emitter structures connected to respective ones ofthe optical waveguides, each optical emitter structure configured toemit a light beam from the photonic substrate toward an emittingaperture; and an optical power distribution network optically connectinga light source to the plurality of optical waveguides, said opticalpower distribution network including a plurality of switches; whereinsaid switches are configured such that, over at least a first timeinterval, optical power emitted from the light source that enters theoptical power distribution network in different time slots within thefirst time interval will be emitted from different subsets of theplurality of optical emitter structures toward the emitting aperture. 2.The optical structure of claim 1 wherein the plurality of switches areorganized into levels of switches and switches at a same level are allswitched simultaneously.
 3. The optical structure of claim 1 wherein theplurality of optical emitter structures are arranged along a common arc.4. The optical structure of claim 1 wherein the plurality of switchesare organized into levels and switches at one level operate at a speeddifferent from the speed of operation for switches at a different level.5. The optical structure of claim 4 wherein the switches proximate tothe plurality of optical emitter structures operate at the slowestspeed(s).
 6. The optical structure of claim 1 further comprising anoptical element positioned in the emitting aperture in the optical pathof the emitted optical power.
 7. The optical structure of claim 6wherein the optical element comprises a lens.
 8. The optical structureof claim 7 wherein the optical element further comprises a grating andthe grating is positioned in the optical path of the emitted opticalpower between one of the plurality of optical emitter structures and thelens.
 9. The optical structure of claim 7 wherein the lens is configuredand positioned to focus optical power from each one of the plurality ofoptical emitter structures.
 10. The optical structure of claim 6 whereinthe optical element is configured and positioned to receive opticalpower from each one of the plurality of optical emitter structures. 11.The optical structure of claim 6 wherein the optical element comprisesat least one grating.
 12. The optical structure of claim 1 wherein theoptical power distribution network is a tree network and the switchesinclude at least one of: one or more 1×2 switches, one or more 1×3switches, one or more 1×4 switches, one or more 2×2 switches, or one ormore 2×3 switches.
 13. The optical structure of claim 1 wherein theoptical power distribution network and the plurality of optical emitterstructures are fabricated on the photonic substrate.
 14. The opticalstructure of claim 1 wherein the optical power distribution network, theplurality of optical emitter structures, and the light source are allresident on the photonic substrate.
 15. The optical structure of claim 1further comprising a coherent receiver.
 16. The optical structure ofclaim 1 wherein at least one of the switches is one selected from thegroup consisting of thermo-optic and electro-optic switch(es).
 17. Theoptical structure of claim 1 wherein each one of the plurality ofoptical emitter structures is one selected from the group consisting of:an optical grating, plasmonic emitter, metal antennae, and mirror facet.18. The optical structure of claim 1 further comprising a plurality offocusing gratings, where two or more of the plurality of optical emitterstructures is each configured to direct optical power to a correspondingone of the plurality of focusing gratings.
 19. The optical structure ofclaim 1 wherein the plurality of optical emitter structures areconfigured to emit from positions arranged over two dimensions of aplane.
 20. The optical structure of claim 19 further comprising anoptical element positioned in the optical path of the emitted opticalpower and configured to produce a substantially flat focal planecoincident with the plane over which the positions of the plurality ofoptical emitter structures are arranged.